This invention relates to traction drive transmissions and more particularly, it concerns improvements in torque body constructions used in continuously variable traction drive transmissions and by which normal forces developed between rolling traction surfaces are varied to account for varying torque loads.
In U.S. Pat. Nos. 4,112,779, 4,112,780 and 4,152,946 several continuously variable transmission embodiments are disclosed in which three frame supported working or torque bodies operate to transmit a mechanical power input to a rotatable output at infinitely or continuously variable speed ratios within the design range of the particular transmission embodiment. In the transmissions of this general class, two of the torque bodies are in rolling friction contact with each other at two points of contact as a result of one of the two bodies being of a biconical configuration to define oppositely convergent traction surfaces of revolution about one axis and the other of the two bodies taking the form of a rotatably coupled pair of rings defining complementary traction surfaces about another axis inclined with respect to and intersecting the one axis. The rings are adjustable in a manner to vary the radius ratio of the contacting traction surfaces and thus attain the continuously variable speed ratio for which the transmission is primarily intended.
In a commonly assigned U.S. patent application Ser. No. 06/005,605, filed Jan. 22, 1979, by Harvey N. Pouliot, now U.S. Pat. No. 4,280,369, various embodiments of a ball/ramp system are disclosed for retaining the engaged rolling surfaces in contact under normal force loads generally proportional to the output torque load of the transmission. In the system disclosed in this application, the biconical torque body of the transmission is provided as an assembly of two conical members supported by a common central shaft in a manner permitting axial separation of the conical members along the shaft and also permitting for rotation of the cone members relative to each other and relative to the shaft. The shaft is coupled either directly or indirectly to the transmission output load and carries a central splined ring or sleeve between the base ends of the cone members. The sleeve as well as the base ends of the respective cone members are engaged by ball/ramps so that torque transmitted between the cones and the shaft will result in a force tending to separate the cones, the separating force being a function of the torque load on the shaft. As pointed out in the application, the potential exists for an unwanted torque path between the cone members such that under conditions of zero or near zero output loading, the ball/ramp system can become self-energizing to bind the conical members against the traction rings with which they cooperate, a situation which can result in a lock-up of the transmission components. This problem is solved in accordance with certain of the embodiments disclosed in the application by providing one of the cone members with a lead bias in a way that some force will be transmitted by the ball/ramp at all times and thus avoid the effects of a torque path between the individual cone members.
In a commonly assigned U.S. patent application Ser. No. 06/077,833, filed Sept. 21, 1979, by Yves Jean Kemper, now U.S. Pat. No. 4,277,982, a biconical torque body construction is disclosed in which the central load coupled supporting shaft is eliminated. In this instance, the biconical body is constituted by two conical members connected at their bases for axial and rotational movement relative to each other and in which one of the two cone members is coupled for torque transmission with the output load of the transmission unit. The one cone so coupled with the load is provided with a pilot cone extending to the small end of the other cone and coupled for torque transmission therewith through a ramp assembly. With variations in output load, the other cone member will react through the ramp assembly to develop the axial separating force by which both cone members are retained in rolling friction engagement with the appropriate working body of the transmission. By avoiding the provision of a central shaft, the problems associated with deflection of the central shaft and the unwanted torque path between the cone members are avoided.
While the normal force developing systems disclosed in these prior applications represent significant advances toward the solution of problems experienced with traction drive transmissions of the type under discussion, there is need for improvement particularly in the provision of a biconical torque transmitting body which may be easily fabricated and assembled to include an effective and reliable normal force developing system.